Method of and apparatus for enameling



Oct. 21, 19 1. w. c. JoHNsgm 2,259,935

METHOD OF AND APPARATUS FOR ENAMELING Filed Aug. 2'7, 1940 INVENTOR.

' WALLACE C.JOHNSON BY M, r QM ATTORNEYS l 'atented Oct. 21, 1941 UNITEDSTAT E's, PAT-E NT OFFICE METHOD OF AND APPARATUS FOR ENAMELING Wallace0. Johnson, Shaker Heights, Ohio Application August 27, 1940, Serial N0.354,418

12 Claims.

This invention relates as indicated to a method of and apparatus forenameling and more particularly to the enameling of non-metallicarticles which may, on account of'the nature of the material from whichthey are made, not be, fired in a conventional muflie in accordance withthe customary process of porcelain enameling.

In the enameling of non-metallic objects, the.

nature of the material from which the same are made introduces otherdifficulties not encountered in the enameling of metallic articles. Inother words, it is of exceedingly greater dimculty to secure acontinuous and uniform enameled finish coat on a non-metallic article,which is many times full of pores and gas occlusions and subject todeterioration under the influence of vthe-heat employed in fusing theenamel, than the description proceeds.

To the accomplishment of the foregoing and related ends, said inventionthen comprises the features hereinafter fully described andparticularly' pointed out in the claims, the following description andthe annexed drawing setting forth in detail certain illustrativeembodiments of the invention, these being indicative however of but afew of the various ways in which the principle of the invention may beemployed.

In said annexed drawing:

Fig. 1 is a side elevational view showing somewhat diagrammatic anapparatus embodying the process of my invention; j

Fig.2 is'a fragmentary plan view partially in section of that portion ofthe apparatus illustrated in Fig. 1 indicated by the bracket 2; and

Fig. 3 is a fragmentary plan viewof that portion of the apparatusillustrated in Fig. 1 embraced by the bracket 3.

Referring nowmore specifically to the drawing, and-more especially toFig. 1, the apparatus .carried out, includes an endless conveyor belt orchain 4 trained about spacedsprockets 5 so that on its upper run '6 theconveyor may carrya plurality of work objects 1 past the varioustreating stages.

Any suitable form of conveyor may be employed, the endless belt typebeing illustrated for purposes of convenience. In the apparatus whichhas been constructed and operated successfully, the conveyor is drivenby means of a variable speed motor so that the speed of travel of thework objects past the several stages" may be controlled. Such avariation in the speed of the conveyor is usually not necessary afterthe apparatus has once been adjused to handle a particulartype ofmaterial. Itwill generally be found that with the treatingstagesarranged in the manner and for the purpose hereinafter more specificallydefined, andwhen treating a material such as Haydite-block for example,the conveyor may be set to operate at a speed of about two feet perminute, and such speed then progresemployed in enameling furnaces inorder that it v may. withstand high heat without deterioration. Theconveyor chain or belt 4 may be of any desired width so as toaccommodate at least one row of the work objects to be enameled. In thea commercial installation which has been made of formed. These steps inthe process can best be ditions of operation, one ormore-rows of work.

objects may be simultaneously passed through the apparatus.

. As above indicated, theconveyor is designed to substantiallycontinuously move thework' objects at the stated-sp'eed past a pluralityof stages where various steps in my process are perdefined by havingreference to the individual stages which, for purposes of convenience inidentification in the following description, will be designated by theo'rdinals 8 to- IG inclusive.

The drier stage 8 At this stage, there is provided a hood generallyindicated at, the-same being provided with open ends just sufilclent topermit the pase gates to automatically open'when engaged bya 1 workobject, and to close behind the work object as the same passes into thehood ll. It will generally be found more economical, however, especiallywhen treating work objects of uniform size, to place the same in closelyabutting relation on the conveyor 4 as illustrated in Fig. 1, and tothen conform the opening ID to the cross-section of the work objects sothat they, in passing into the hood I1, act as a seal for such opening.

Positioned in the hood I1 is a burner I9 utilizing conventional fuels,such as hydrocarbon gas or oil, for the purpose of preheating and dryingthe work objects. The hood I1 is provided with a stack 20 through whichthe products of combustion and the moisture eiiminated'from the workobjects may pass. The temperature maintained in the drier 8 should besufficiently high so that in the interval during which the work objectspass therethrough, the surface area thereof to be enameled arethoroughly dried. This is necessary in order that in the succeedingstages of the process, especially during the firing of the finish coat,there will be no liberation of moisture from the work object which, inpassing upwardly through the finish coat while the latter is in a moltenstate, would puncture or otherwise break the same. In the enameling ofbuilding units, such as Haydite block, cement block, cinder block andthe like, this drying may be effected by maintaining a temperature onthe order of 2000 F. in the predrier 8. Such temperature will besatisfactory when the speed of the conveyor is two feet per minute, andwhen the drying stage 8 is four feet long so that the work objects arein the drier for a period of two minutes. Changes may be made in thetemperature and speed correlating the same to arrive at substantiallythe same results.

Mounted adjacent the discharge opening of the hood I! is a blow pipe 2|so positioned as illustrated in Figs. 1 and 2 that a stream of airdischarged thereby will sweep across the upper surface of the workobjects asthey are discharged from the hood IT. This air blast isefiective to remove foreign articles, such as dust, dirt and the like,which may be lying on the surface of the work object to be enameled. Itis, of course, desirable that all loose particles, such as dust, dirtand even small pieces of the work object which may have been loosened inthe predrying chamber, be removed before the application of any of theprotective coatings to the work.

Grip coat application stage 9 At this stage, a so-called grip coat'isapplied to the work objects by any conventional means. This grip coat isnecessary and. essential for certain types of material, and has twoprimary functions. First, it fills the irregular surface of the roughblocks and makes a smoother finish for the enamel to adhere to, andsecond, it serves to seal the work surface being enameled so thatliberation of occluded gases or moisture in the form of steam from thework surface and-through the finish coat will be reduced to a minimum.This grip coat may be anyof a wide variety of suitable materials. I havefound that in the enameling of Haydite block, for example, that theagsufficient" to produce aspreadable mass, gives:

satisfactory results. The principal constituent of the grip coat shouldbe a material which will fuse at the temperature to which the worksurface is later subjected so that a fused bond may be establishedbetween the grip coat and the work surface. There are a variety ofmaterials available and well-known to those familiar with the art whichhave these properties, and any of them may be used with satisfaction. Awater solution of sodium silicate is a convenient and relativelyinexpensive medium by which the grip coat may be applied to the work.

Any one of a variety of well-known ways may be employed in theapplication of this grip coat to the work object. A transfer roll may beused, or more conveniently, a brush, such as 22, lllustrated in Figs. 1and 2. The brush 22 is what is commonly termed an .end brush in that thebody of the brush is circular, supported by a hollow shaft extendingaxially thereof with the bristles of the brush extending in the oppositedirection from the circular head. The grip coat, in a fluid state, isfed to the bristles through the hollow supporting handle or shaft, andthe brush simultaneously rotated to spread such grip coat evenly overthe work surface. The diameter of the brush should only be slightlygreater than the Width of the work pieces so that the entire width ofthe work may be covered without wastage of the grip coat.

The thickness at which this grip coat is applied to the work will varyaccording to the nature of the work surface, it being kept in mind thatone of its functions is to provide a smooth surface for the reception ofthe ultimate finish coat. Thus, when operating upon building units madeof Haydite or cinders or the like, the surface of the block may containa large number of voids and small openings. In order to secure a smoothfinish coat, the grip 'coat should be applied to the work surface withsufficient thickness so as to fill all of the voids on the work surface.

When using a mixture such as sodium silicate and I-Iaydite dust or thelike, some difficulty may be encountered in spreading the grip coatuniformly over the work surface especially since the latter is in aheated state as a result of having just passed through the predrier 8.The heated surface of the work unit has a tendency to very rapidlyabsorb the moisture content of the grip coat, and thus interfere withits uniform distribution. This difliculty may be overcome by entraininga small amount of water, either in the form of finely divided water orsteam, in the air stream of the cleaning jet 2|. This moisture will beabsorbed only by an extremely thin surface layer of the work pieces, andwill subsequently be evaporated in the grip coat'drier presently to bedescribed.

Grip coat drying stage 10 At this stage, there is provided a hood 23generally similar to the hood I! at the predr'ying stage 8. A burner 24or other suitable means may be provided in the hood 23 for the purposeof generating suflicient heat and agitation of the air therein to effecta drying of the grip coat. Here again, that must be observed-to insurethat the grip-coat will be thoroughlydry so that no moisture will begiven off by it in the form of steam to rise upwardly through andpuncture the finish coat ultimately fused thereover. The size of thehood 23, i. e. its extent in the direction of travel of. the conveyor,and accordingly the time during which the work objects are in the hood23, will determine the temperature to be maintained in such hood. In thecommercial Finish coat spray stage 11 While this stage has, in thedrawing, been represented diagrammatically by a spray nozzle for theapplication of the finish coat to the work objects, nevertheless, itwillbe found that in actual practice a conventional spray booth such as isemployed in enameling plants will be most suitable in that the areawhere the spraying is performed is laterally enclosed and vented toprevent scattering of the spray over areas other than the surface of thework to be enameled. One or more spray guns properly arranged anddirected at the work may be provided so that as a continuous line ofwork objects are moved past the spray stage they will receive a uniformcoating of enamel.

At this point, it may be well to point out that in the enameling ofbuilding units of the character to be used in walls and the like, amottled appearance is generally more pleasing to some people than asolid color, and in the production of such an appearance, an underlyingcontinuous finish coat of one color may be applied by one or more sprayguns, and thereafter a so-called splatter coat may be applied by meansof a splatter gun in a color contrasting to the underlying coat, and thevariegated appearance thus produced.

The enamel slip which is applied 'to the Work at the stage II willdesirably be formed of an enamel which has two principal characteristicsin addition to the other characteristics generally found desirable inenamels. First, the enamel should have a relatively low fusing point,and second, the enamel should have a relatively low coefiicient ofthermal expansion. These two characteristics are desirable for thereasons that in the enameling of non-metallic objects, such as buildingunits, it is desirable to keep down as low as possible the ultimatetemperature to which the work object is subjected during the firing orfusion of the finish coat, and secondly the coefiicient of thermalexpansion of the nonmetallic work objects is usually considerably lessthan the coefficient of thermal expansion of metallic articles, so thatan enamel which might work satisfactorily on a metallic article mighthave too high a coefficient of thermal expansion, and accordingly tearor crack when applied to a non-metallic work object.

-While,it is desirable, as indicated above, that the enamel have arelatively low fusion point, nevertheless, enamels or glasses which havea relatively high fusion point may be used depending on the nature ofthe work being enameled and accordingly the degree to which the same maybe raised in temperature. In the enameling of Haydite blocks, such asconventional building blocks, I have secured successful results by theuse of an enamel which is fundamentally similar to the glasscommercially known as Pyrex. Successful results have also-been securedwith the use of glazes of the type employed for the surfaceornamentation of glass objects. These are representative of the widelimits in so far as melting point is concerned ofthe glass or enamelwhich may be used;

f 25, the flame and other products of combustionthe temperatureconditions as above specified After leaving the finish coat spray stageII, it is especially important in the enameling of non-metallic objectsto have the work piece and the grip and finish coats thoroughly drybefore an attempt is made to fuse or fire the same.

Finish coat dry and preheating stage 12 In order that the grip coat,finish coat, and

the underlying work surface may be thoroughly dry, 1. e. free frommoisture as well as occluded gases which might pass upwardly through thefinish coat during the firing operation to disrupt the same, the workpieces are led through an elongated tunnel in which they are subjectedto progressively higher temperatures. This predryi'ng or preheatingstage may be conveniently provided by leading through a tunnel, such asfrom the firing stage l3. By providing a stack such as 25 at the forwardend of the tunnel l2,

may be conveniently obtained. In order to observe the temperatureconditions which will be maintained in the tunnel l2, thermo couples,

such as 21, 28, 29 and 30 may be provided at convenient uniformly spacedpoints, and the damper in the stack 26 adjusted so as to maintain thedesired temperature at such points.

Bafiles in the tunnel might also be resorted to if necessary to securethe proper control. The temperatures in the various thermo couple stageswhich I have found to produce satisfactory reto, satisfactory resultshave been secured by the use of a tunnel I2 which is approximatelyfourteen feetlong with a conveyor speed of two feet per minute so thatthework objects are in the drying and preheating tunnel l2 for a periodof approximately seven minutes. lateral walls of the tunnel I 2laterally adjustable, i. e. adjustable on a line transversely of thedirection of travel of the conveyor 4, the size of the tunnel may bealtered to accommodate various widths of work pieces. This is desirablesince the interibr space of the drying and preheating tunnel if made toconform rather closely to the cross-section of the work pieces willresult in more eflicient operation since the stream of gases flowingthrough the tunnel will be in more intimate contact with the worksurface, and a greater turbulence set up in such stream.

Flash fire stage 13 the work pieces are led past the burner, and,

other factors have a bearing on the amount of heat required at the flashfire stage. Tempera- 'tures on the order of those indicated have beenattained in the flash fire stage of the finish coat on Haydite block,for example, ina burnerutilizing from about 750 to 1500 cubic'feet perhour of a mixture of artificial and natural gas having By making the Oneform about 750 B. t. u. per cubic foot. In the operation of thecommercial installation under the condition above specified, the averagetemperatures at the thermo coupled stations 21, 28, 29 and 30 were 760F., l1l5 1"., 1500 F., and 2000 F., respectively.

The enamel used will, of course, fuse at a temperature much less than2800 F. However, this high temperature is necessary and desirable inorder that the finish coat may be thoroughly fused and thus bonded tothe work without an excessive heating of the work object. By utilizing atemperature on the order of 2800 F., complete fusion of the vitreous orporcelain enamel finish coat may be secured in periods not substantiallyin excess of one minute. I have operated the commercial apparatusreferred to above under such conditions that a unit area of work surfaceis subjected to the high temperature fiame for a period of thirtyseconds, and for as short a time as fifteen seconds and even eightseconds with thorough fusion and satisfactory bond of the finish coat tothe work surface.

Shock chilling stage 14 As previously indicated, many porcelain enamelswith a fusion range low enough to be satisfactorily employed in theenameling of non-metallic articles have a coefficient of thermalexpansion considerably greater than the coefficient of thermal expansionof the work object to which the enamel is applied. This fact, coupledwith the fact that the enamel passes through a very much greatertemperature than does the less highly heated work surface, has'atendency to cause checking or crazing of the enamel upon cooling. I havefound that thiscan be satisfactorlly overcome by shock chilling theenamel in its very highly heated state as it leaves the flash firingstage [3. This is accomplished by provoking a stream of water onto themolten finish coat immediately as it issues from the flash fire stage.Successful results have been secured by regulating the supply of waterto such an extent that small pools of water actually rest on the surfaceof the very highly heated enamel finish coat. This shock chilling iseffective to eliminate the crazing of the finish coat which wouldotherwise occur. This is an important step in my process.

Water quench blow-o1? 15- In order that the water quench or shockchilling may be stopped with sufficient heat remaining in the worksurface being enameled and in the finished coat itself, so thatsubsequent annealing of the finish coat may take place, it is necessarythat the water admitted to the highly heated finish coat be removedbefore the finish coat has cooled to too great an extent. This isconveniently accomplished by an air jet at stage I directed across theenamel face of the work surface to blow all moisture therefrom, and topermit the cooling under atmospheric conditions of the work surfacethereafter.

The cooling stage 16 After the shock chilling stage, above referred to,the conveyor 4 carries the work pieces through a cooling zone which maybe opened to the thereof at the proper rate so that annealing of thefinish coat in the manner above described may take place, and so thatthe finish coat does not cool too rapidly in order to produce furtherchecking or crazing.

The process above described may be varied from the precisely statedprocedure in order to adjust the same to the requirements of theparticular material being enameled. Thus, for example, when anon-metallic article is enameled which has a glazed coating, i. e. asurface for the reception of the enamel, which surface is sufficientlydense and smooth so that the two requirements for a grip coat as aboveexplained are not present, then such grip coat may be omitted. Otherchanges in the described process may be made in order to adapt the sameto variation in properties of the particular material being enameled.

Other modes of applying. the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

I therefore particularly point out and distinctly claim as my invention:

1. The method of vitreous enameling nonmetallic articles which comprisessubjecting the surface thereof to be enameled to the followingsuccessive steps; a finish coat of vitreous enamel; a drying andpreheating of such finish coat; a flash fire at a temperature on theorder of about 2800 F. for a period on the order of about 30 seconds;and a shock chilling of the finish coat while the latter is in highlyheated condition.

2. The method of vitreous enameling nonmetallic articles which comprisessubjecting the surface thereof to be enameled to the followingsuccessive steps; a, grip coat to seal the work surface; a drying of thegrip coat; a finish coat; a drying and preheating of the finish coat;and a flash fire at a temperature high enough to fuse the finish coat ina period not substantially in excess of one minute.

3. The method of vitreous enameling nonmetallic articles which comprisessubjecting the surface thereof to be enameled to the followingsuccessive steps; a grip coat to seal the work surface; a drying of thegrip coat; a finish coat; a drying and preheating of the finish coat; aflash fire at a temperature high enough to fuse the finish coat in aperiod not substantially in excess of thirty seconds; and a shockchilling of the finish coat while the latter is in highly heatedcondition.

4. The method of vitreous enameling nonmetallic articles which comprisessubjecting the surface thereof to be enameled to the followingsuccessive steps; a predrying; a grip coat to seal the work surface; adrying of the grip coat; a

finish coat; a drying and preheating of the finishcoat; and a flash fireat a temperature high enough to fuse the finish coat in a period on theorder of about thirty seconds.

5. The method of vitreous enameling nonmetallic articles which comprisessubjecting the surface thereof to be enameled to the followingsuccessive steps; a predrying; a grip coat to seal the work surface; adrying of the grip coat; a finish coat; a drying and preheating of thefinish coat; a flash fire at a temperature high enough to fuse thefinish coat in a period on the order of about thirty seconds; and a,shock chilling of the finish coat while the latter is in highly heatedcondition.

6. The method of vitreous enameling nonmetallic articles which comprisessubjecting the surface thereof to be enameled to the followingsuccessive steps; a predrying at a temperature on the order of about2000 F. for a'period on the order of about two minutes; a cleaning toremove foreign material; a grip coat to seal the work surface; a dryingof the. grip coat at a temperature on the order of about 1400 F. for aperiod on the order of about two minutes; a finish coat; a, drying andpreheating of the finish coat; a flash fire at a temperature on theorder of about 2800 F. for a periodon the order of about thirty seconds;a shock chilling of the finish coat while the latter is in highly heatedcondition; and an air blast to remove the shock chilling medium andpermit the fused finish coat to cool under atmospheric conditions.

'7. In app'aratusfor the vitreous enameling of non-metallic articles thecombination with conveyor means for carrying the work objects past aplurality of treating means, for the work surface to be enameled, saidmeans being adjacent such conveyor and respectively comprising;

means for applying a finish coat to the work face to be enameled, saidmeans being adjacent such conveyor and respectively comprising; meansfor applying a grip coat where a material effective to seal the worksurface and increase the adhesion of the enamel thereto is applied tothe work surface; means for drying said grip coat; means for applying afinish coatto the work surface; means for drying and preheating thefinish coat; and a flash fire means where the finish coat is fused bybeingsubjected to a temperature high enough to fuse the finish coat in aperiod not substantially in excess of one minute.

. 9, In apparatus for the vitreous enameling of non-metallic articles,the combination with conveyor means for carrying the work objects past aplurality of treating means for the work surface to be enameled, saidmeans'being adjacent such conveyor and respectively comprising; apredrying means; a grip coat application means where a materialeffective to seal the work surface and increase the adhesion of theenamel thereto'is applied to the work surface; a grip veyor means forcarrying the work objects past a plurality of treating means for thework surface tobe enameled, said means being adjacent such conveyor andrespectively comprising; a grip coat application means where a materialeffective to seal the work-surface and increase the adhesion of theenamel thereto is applied to the work surface; a grip coat drying means;a finish coat station where the finish coat is applied to the worksurface; a drying and preheating means where the finish coat is driedand preheated; a flash fire means where the finish coat is fused bybeing subjected to atemperature high enough to fuse the finish coat in aperiod not substantially in excess of about thirty seconds; and a waterquench means where the finish coat while in highly heated condition issubjected to shock chilling.

11. In apparatus for the vitreous enameling of non-metallic articles,the combination with conveyor means for carrying the work objects past aplurality of treating means for the work surface to be enameled, saidmeans being adjacent such conveyor and respectively comprising; apredrying means; a grip coat application means where a materialeffective to seal the work surface and increase the adhesion 'of theenamel thereto is applied to the work surface; a grip coat drying means;a finish coat means where the finish coat is applied to the worksurface; a drying and preheating means where the finish coat is driedand preheated; a flash fire means where the finish coat is fused bybeing subjected to a temperature high enough to fuse the finish coat ina period on the order of about thirty seconds; and a water quench meanswhere the finish coat while in highly heated condition is subjected toshock chilling.

12. In apparatus for the vitreous enameling of non-metallic articles,the combination with conveyor means for carrying the work objects past aplurality of treating means for the work surface to be enameled, saidmeans being adjacent such conveyor and respectively comprising; apredrying means where the work surface is subjected to a temperature onthe order of about 2000 F. for a period on the order of about twominutes; a cleaning means where the work surface is freed of foreignmaterial; a grip coat application means where a material effective toseal the work surface and increase the adhesion of the enamel thereto isapplied to the work sur-' about two minutes; a finish coat means wherecoat drying means; a finish coat station where thirty seconds.

10. In apparatus for the vitreous enameling of non-metallic articles,the combination with conthe finish coat is applied to the work surface;a drying and preheating means where the finish coat is dried andpreheated; a flash fire means where the finish coat is fused by beingsubjected to a temperature on the order of about 2800 F. for a period onthe order of about thirty seconds;

. a water quench means where the finish coat while in highly heatedcondition is subjected to shock chilling; and an air blast meanswherethe water quench is blown off from the work to permit the fusedfinish coat to cool under atmospheric conditions.

WALLACE C. JOHNSON.

